1. Description of Related Prior Art
The disclosure relates to high-power laser and amplifier φTB systems configured to emit radiation in a fundamental mode. In particular the disclosure relates to a method and apparatus for suppressing high order modes in multimode fiber-based high power fiber laser systems.
2. Background of the Disclosure
The modern industrial trends demand scaling the power levels of fiber lasers operative to output radiation in a fundamental mode. The scaling of the power in the fundamental mode is, however, limited by two major phenomena: nonlinear effects and mode coupling with high order modes (“HOM”).
Propagating intense light through long fibers leads to nonlinear distortions such as stimulated Raman scattering, stimulated Brillouin scattering, self-phase modulation, and related parametric processes. Mitigating these effects requires fibers in which the optical mode occupies a large modal area, and hence is less intense. One of the development efforts in the field of high-power fiber lasers has focused on large-mode-area (LMA) fibers characterized by a relatively high threshold for nonlinear effects.
As to the mode coupling, in ideal multimode (“MM”) fiber, modes remain independent of each other as they propagate. Because each mode travels with a different group velocity, when even a few high order modes (“HOM”) excited at the fiber input, the output signal can be degraded due to intermodal dispersion. In a real-world fiber imperfections such as microbends and geometric irregularities lead to an exchange of power between fundamental and HO modes. The mode coupling results in a deterioration of system performance and reduced output power coupled in the fundamental mode. A number of concerned efforts have been directed to minimize mode coupling. Yet this problem persists and needs to be addressed again and again.
It is therefore desirable to provide a new method for minimizing a coupling mode coefficient in high power fiber laser systems.
A further need exists for an apparatus configured to carry out the disclosed method.